Regarding such a lithium-ion secondary battery, JP H05(1993)-290844 A, for example, discloses the use of a mixture of natural graphite and artificial graphite as a negative electrode material capable of storing and releasing lithium, for a lithium secondary battery using a LiPF6-containing electrolyte solution.
This publication describes that natural graphite (rhombic structure), which tends to overreact with LiPF6 at high temperature, is mixed with artificial graphite (hexagonal structure), which has low reactivity with LiPF6, so that natural graphite and LiPF6 can be inhibited from excessively reacting with each other.
JP 2010-97696 A discloses the use of a negative electrode active material in which amorphous carbon is coated or adhered to the surfaces of graphite particles.
In addition, JP 2009-64574 A discloses that a plurality of negative electrode active material layers are formed on a negative electrode current collector so that a far side thereof from the negative electrode current collector shows higher charge rate performance than a near side thereof to the negative electrode current collector. This publication also discloses that artificial graphite is used as the negative electrode active material in the near side to the negative electrode current collector and natural graphite is used as the negative electrode active material in the far side from negative electrode current collector.